The overall emphasis of this renewal application is to understand the molecular pathways that control cardiac gene expression and the hypertrophic growth of the myocardium. The focus of this proposal is to analyze the GATA4, 5, and 6 transcription factor family as regulators of both embryonic heart development and during pathological and physiological growth of the adult heart. GATA factors are known to directly regulate the expression of most cardiac-expressed structural genes, thus facilitating the differentiation of cardiomyocytes during early heart development. In the adult heart, GATA4 and GATA6 transcription factors are re-employed where they function as important regulators of the hypertrophic gene program in response to pathophysiologic stimulation. Indeed, the hypertrophic response of the adult heart involves re-expression of many fetal genes, suggesting that the developmental and disease gene programs share common regulatory events, potentially through GATA4/5/6. Our unifying hypothesis states that GATA4, 5, and 6 are required for both the establishment and maintenance of the cardiac differentiation-specific gene program as well as the growth response of the adult heart during stress stimulation. Previous attempts to define the importance of GATA factors as regulators of the cardiac gene program involved a traditional loss-of-function approach in gene-targeted mice. However, this approach was largely uninformative due to early embryonic lethality and genetic redundancy issues. Here Cre-lox technology will be employed in conditionally targeted GATA4 and GATA6 mice to produce tissue-specific and temporally-regulated gene inactivation in the developing and adult heart. Using these genetically modified models, specific aim #1 will investigate the importance of GATA6 in mediating pathophysiologic growth of the adult heart. Specific aim #2 will determine if conditional disruption of Gata4 and Gata6 together in late embryonic development affects subsequent neonatal heart hypertrophy and the hypertrophic growth response of the adult heart following stress stimulation. Specific aim #3 will determine if Gata4/6 gene deletion in the very early heart-forming region disrupts cardiomyocyte differentiation and/or heart tube morphogenesis. Finally, specific aim #4 will investigate the issue of redundancy between GATA4 and GATA6 in the adult heart using a genetic complementation strategy. Taken together, an understanding of the regulatory networks that control cardiac differentiation-specific gene expression at steady state and in response to stress will be instrumental in dissecting the transcriptional networks that underlie congenital abnormalities of the heart, as well as diseases of the adult heart. PUBLIC HEALTH RELEVANCE This application will investigate the ability of GATA4/5/6 zinc finger-containing transcription factors to directly regulate the differentiated state of the heart. Cardiac- expressed GATA transcription factors have been shown to bind to the promoters of most structural and regulatory genes expressed in the heart, suggesting that they might underlie the entire heart-specific gene program. Here we will specifically address this hypothesis by generating genetically altered mice with conditional deletion of Gata4 and/or Gata6 from the developing or adult heart. This approach should determine if the cardiac- expressed GATA transcription factors control the early differentiation of cardiac myocytes in the heart, as well as their role in re-programming gene expression in the adult heart following stress stimulation, permitting hypertrophic growth. An elucidation of these regulatory relationships is of considerable disease relevance.